1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and method of fabricating the same, and more particularly, a liquid crystal display (LCD) device having a patterned spacer for keeping a cell gap and a method for fabricating the same.
2. Discussion of the Related Art
In general, liquid crystal display (LCD) devices have been developed for displaying images having low power consumption and portability characteristics. Currently, liquid crystal cells must be manufactured using LCDs for displaying images. The liquid crystal cells have array and color filter substrates and a liquid crystal material layer between the array and color filter substrates. Transparent electrodes are commonly formed on each of the array and color filter substrates to induce an electric field to the liquid crystal material layer by application of a voltage. An amount of transmitted light is controlled by the applied voltage, and images are displayed by a light shutter effect. An active matrix liquid crystal display device (AMLCD) that has a switching element at each pixel has been developed having superior resolution and an improved ability to display moving images. The liquid crystal display (LCD) device can be fabricated through an array substrate forming process, a color filter substrate forming process, and a liquid crystal cell forming process. Array elements, such as switching elements and pixel electrodes, are formed during the array substrate forming process, and color filters and common electrodes are formed during the color filter substrate forming process. The liquid crystal material is injected into a space between the array and color filter substrate during the liquid crystal cell forming process. The liquid crystal cell forming process is relatively simple compared to the array substrate and color filter forming processes. The liquid crystal cell forming process mainly comprises an alignment forming process, a cell gap forming process, a cell cutting process, and a liquid crystal material injection process. A liquid crystal display panel is completed by the liquid crystal cell forming process.
FIG. 1 is a cross sectional view of a liquid crystal display (LCD) device according to the related art. In FIG. 1, upper and lower substrates 10 and 30 are spaced apart from each other and a liquid crystal material layer 50 is interposed between the upper and lower substrates 10 and 30. A gate electrode 32 is formed on a transparent substrate 1 of the lower substrate 30, and a gate insulating layer 34 is formed on entire surface of the transparent substrate 1. A semiconductor layer 36 that has an active layer 36a and an ohmic contact layer 36b are sequentially formed over the gate electrode 32. Source and drain electrodes 38 and 40 are formed on the semiconductor layer 36, and a channel “ch” that exposes a portion of the active layer 36a is formed between the source and drain electrodes 38 and 40. The gate electrode 32, the semiconductor layer 36, the source electrode 38, the drain electrode 40, and the channel “ch” form a thin film transistor “T.” A gate line (not shown), which is connected to the gate electrode 32, is formed along a horizontal direction, and a data line (not shown), which is connected to the source electrode 38, is formed along a vertical direction. The gate and data lines (not shown) cross each other to define a pixel region “P,” and a passivation layer 42 that has a drain contact hole 44 is formed over the thin film transistor “T.” A pixel electrode 48 that is connected to the drain electrode 40 through the drain contact hole 44 is formed within the pixel region “P.” A color filter 14 is formed on a bottom surface of the upper substrate 10, and corresponds to the pixel electrode 48. A black matrix 12 is formed within a boundary region between neighboring sub-color filters to prevent light leakage and light infiltration into the thin film transistor “T.” A common electrode 16 is formed beneath the color filter 14 for applying a voltage, and a seal pattern 52 is formed along edges of the lower substrate 30 to prevent the injected liquid crystal material from leaking. Ball spacers 54 are disposed between the upper and lower substrates 10 and 30 to maintain a uniform cell gap along with the seal pattern 52. An upper alignment film (not shown) and a lower alignment film (not shown) may further be formed between the common electrode 16 and the liquid crystal layer 50 and between the pixel electrode 48 and the liquid crystal layer 50, respectively. The ball spacers 54 are commonly formed of an elastic material, such as glass fiber and organic material, and are randomly disposed between the upper and lower substrates 10 and 30. However, alignment layer inferiority may occur due to movement of the ball spacers 54, and light leakage may occur around the ball spacers 54 due to an absorption power between the ball spacers 54 and liquid crystal molecules of the liquid crystal material layer 50 adjacent to the ball spacers 54. In addition, it is difficult to maintain a stable cell gap when the ball spacers 54 are applied to a large-sized liquid crystal display (LCD) device. Moreover, since the ball spacers 54 are electrically conductive and move around between the upper and lower substrates 10 and 30, a severe ripple phenomenon occurs when a screen is touched. Consequently, it is difficult to display high quality images in a liquid crystal display (LCD) device in which ball spacers are used for maintaining a uniform cell gap.
To overcome these problems related to ball spacers, patterned spacers formed at specific locations of the upper and lower substrates by a photolithographic process have been suggested. Accordingly, light leakage can be reduced and a uniform cell gap can be maintained since the patterned spacers are formed within non-pixel regions. In addition, the liquid crystal display (LCD) device can be manufactured to avoid the ripple phenomenon.
FIG. 2 is a cross sectional view of a liquid crystal display (LCD) device having a patterned spacer according to the related art. In FIG. 2, upper and lower substrates 60 and 70 are spaced apart from each other, and a thin film transistor “T” and pixel electrode 72 are formed of transparent conductive material on the lower substrate 70, and are electrically connected to the thin film transistor “T.” A black matrix 62 is formed beneath the upper substrate 60 corresponding to the thin film transistor “T,” and a color filter 64 is formed beneath the upper substrate 60 and the black matrix 62. A common electrode 66 is formed of a same material as that of the pixel electrode 72 beneath the color filter 64. A patterned spacer 74 is formed at a position between the black matrix 62 and the thin film transistor “T” to maintain a uniform cell gap between the upper and lower substrates 60 and 70. A liquid crystal material layer 80 is formed between the upper and lower substrates 60 and 70. In addition, upper and lower alignment layers (not shown) are formed between the common electrode 66 and the liquid crystal layer 80, and the pixel electrode 72 and the liquid crystal layer 80, respectively. The patterned spacer 74 is selectively formed only one of the upper and lower substrates 60 and 70, thereby functioning to maintain a constant cell gap between the upper and lower substrates 60 and 70 after attaching the upper and lower substrates 60 and 70. A height of the patterned spacer 74 is proportional to the required uniform cell gap between the upper and lower substrates 60 and 70. However, as the height of the patterned spacer 74 increases, positional accuracy of the patterned spacer 74 is lowered during the photolithographic process for patterning the patterned spacer 74. Accordingly, a uniform cell gap is not maintained, and inferior rubbing areas increase.
FIG. 3 is a cross sectional view of a rubbing process on the patterned spacer of the liquid crystal display (LCD) device according to the related art. In FIG. 3, a patterned spacer 84 is formed on a substrate 82, and an alignment layer 86 is formed on the entire surface of the substrate 82. During a rubbing process, scratches are formed along a certain direction on a surface of the alignment layer 86. A region “II” of the alignment layer 86 around a base of the patterned spacer 84 is not rubbed, or is irregularly rubbed, thereby generating an inferior rubbing area “II.” As a height “I” of the patterned spacer 84 increases, a width of the inferior rubbing area “II” increases proportionally to the height of the patterned spacer 84. For example, if the height of the patterned spacer 84 is 5 μm, a width of the inferior rubbing is approximately between 7 μm and 8 μm. Accordingly, since the inferior rubbing area “II” is to be covered with a black matrix (not shown) of an opposing substrate, an aperture ratio is decreased due to the additional amount of the black matrix (not shown). In addition, patterned spacers of a height over 5 μm is not proper for photolithographic processing.